I'm with you on "born with": Karen Carpenter, Barbara Streisand and Whitney... we will never have another of any of these ever again. But Louis Armstrong?-- a great great singer and incredible, towering musician by any measure-- doesn't have a naturally "beautiful" voice like them-- he basically plays a kind of voice trumpet using his vocal chords-- which is his personal, developed style- and it is SO compelling and multi-textured. That is practice, baby! That is being comfortable with your instrument and your own stylistic ideas and making stuff up within a style and context. Robert Plant? That is all about the gut of it- the raw impulse. The rock n roll. It's his commitment to the story and the song, but I won't at all agree that he was born with a gorgeous or even naturally interesting voice-- but he has developed a very clear artistic one-- developed-- practiced and imagined. Bob Dylan? He compels a lot of people to buy records and tickets. Tom Waits? Great singing is stylistic and conceptual artistry like Picasso or Sophie Calle. Most important thing about the singing: being comfortable with yourself and accepting who you actually are and loving the imperfections. That is so difficult, I know - it is what we all practice all the time. Once you feel comfortable- it is all about being vulnerable (being totally cool with making mistakes and being imperfect and unbeautiful) in front of many people and making them feel like you trust them with your mistakes and your imperfections and your story. That's the whole thing and the hardest part.
Incidentally, no matter how beautiful the "born with" part, some of those who are most "born with" that impossibly gorgeous tone quality have a much harder time than the rest of us with the accepting of themselves and their imperfections (few, if any in the vocal department) and being vulnerable and ok with who they are. In fact, in the case of Carpenter and Whitney- it killed them —they were unable to sustain this vulnerability.
To your question: "So you have taught someone to change the tone/quality of the voice they were given to the point where ppl pay to hear them sing?" Well, not to change it fundamentally, but to embody it and learn to enhance it and present it with skill and generosity so that others (collaborators, audience members) will be compelled/motivated/helped by its vulnerability, truth, intention and whatever it's about-- this is essentially my job as a teacher of music. Just an FYI--- music is not about who pays to hear it- that is not the mark of its power or greatness. Does it change your life? That's it! (People pay for some crazy bad stuff.)